It is known there are many materials that can not be implanted into the human body. Moreover, with any implant, there is always concern for the possibility of a toxic reaction and a complete rejection of the implant by the body. On the other hand, circumstances do occur when it may be desirable or necessary to implant foreign matter into the body. To help address this need, there has been much research and many development efforts undertaken to determine what implant materials are biocompatible with the human body. Although there have been some successes in solving this problem, much still remains to be done.
In addition to resolving the basic question concerning whether a proposed implant material is biocompatible with the human body, it must also be determined whether the implant material is functional for its intended purpose. To make this functional determination, a major consideration involves whether the implant is to be static or have dynamic characteristics. One set of problems are encountered if the implant structure is to remain static. Quite a different set of problems can be encountered, however, when dynamics are involved and the implant includes a bearing surface which must abut and slide against the bearing surface of another implant. An artificial finger joint is exemplary of such a structure.
In the past, various materials have been suggested for use in the manufacture of body joints. For example, polyethylene and other types of plastic have been tried for such structures. Unfortunately, plastic materials have had only minimal success. Stronger materials, such as metals, have been found to be preferable.
For purposes of manufacturing implants, metals introduce inherent problems which have heretofore obscured their utility. For example, metals tend to corrode in the body. An adverse effect from this fact is that the resultant corrosive products encourage the development of a fibrous membrane of connective tissue which surrounds the implants and is rejected by the body. Also, metals create toxic reactions in the body. It happens, however, some benefit may derive from such toxic reactions. Specifically, it is known that certain metals cause toxic reactions which inhibit the growth of the fibrous membrane. Titanium is such a metal and, despite its potential dielectric, titanium appears to be somewhat biocompatible.
The present invention recognizes that a titanium element, which is properly plated with a protective covering, can be implanted into a human body with tolerable consequences. Specifically, the present invention recognizes that by properly plating or coating the articular surfaces of a titanium implant, any toxic dielectric substance can be hidden from the body's immune discovery system.
As implied above, in addition to the biocompatibility concerns, an implant must also be capable of performing its intended function. Among the various body joints, artificial finger joints present their own unique circumstances. This is so, in part, due to the degrees of freedom which are necessary. For instance, a metacarpophalangeal artificial joint should provide freedom of movement at the joint for the movements of flexion-extension, lateral rotation, and axial rotation. Being more restrictive, an interphalangeal artificial joint need provide for movement in only flexion-extension. In either case, relative movement at the interface between the two bearing surfaces of the artificial joint is necessary. To satisfy these requirements, there must be sufficient durability in the materials for long term usage. Additionally, the artificial joint must be designed with sufficient structural constraints to maintain the relative movement of the joints parts within desired parameters. Also, as stated above, there must be biocompatability between the materials used to manufacture the components of the artificial joint and the human body.
In light of the above it is an object of the present invention to provide an artificial finger joint with components which can be reliably fixed to the skeletal structure of a patient. Another object of the present invention is to provide an artificial finger joint which includes bearing surfaces at the interface between components of the finger joint that are durable and that have useful longevity. Still another object of the present invention is to provide an artificial finger joint which is modular to allow for proper sizing and finger balance. Yet another object of the present invention is to provide an artificial finger joint which is of an all-metal construction. Another object of the present invention is to provide an artificial finger joint which is relatively easy to manufacture and comparatively cost effective.